        html,body {
            margin:0;
            height:100%;
        }
        #shade{
            position:absolute;
            top:0;
            left:0;
            z-index:2;
            width:100%;
            height:100%;
            background-color:#000;
            opacity:0.3;
            /*兼容IE8及以下版本浏览器*/
            filter: alpha(opacity=30);
            display:none;
        }

        #modal {
            position: absolute;
            z-index:3;
            top: 0;
            bottom: 0;
            left: 0;
            right: 0;
            width:200px;
            height:200px;
            margin: auto;
            display:none;
            background-color:#FF0;
        }